Central Glossary

Association study: A study that analyzes whether a certain D N A m a r k e r or a l l e l e is inherited with a particular disease or disorder (e.g., alcoholism) more frequently than would be expected in the general population; the marker or allele does not necessarily play a role in the development of the disease, however, but may just be located adjacent to a gene that contributes to the disease.


Collagen:
The major p r o t e i n component of fibrous connective tissue (e.g., tendons and ligaments); also found in scar tissue.
Congenic strain: A strain of animals, such as mice, in which a D N A segment from one strain has been transferred (or introgressed) into the g e n o m e of a host animal (typically an inbred animal). In a set of congenic strains, the animals are identical with respect to the vast majority of their genetic material and differ only in the introgressed DNA segment.

C y t o k i n e :
A molecule that regulates cellular interactions and cellular functions. Cytokines are produced and secreted by a variety of cells, including immune cells.

Cytosol:
The portion of the cell that contains soluble materials.
C y t o s k e l e t o n : Fiber-like structures within a cell that help give the cell its shape and stability.
Dendrite: A type of thin, branched nerve cell fiber that extends from the n e u r o n ' s body to receive information from other n e u r o n s .

D i a s t o l e :
The time period between two contractions of the heart during which blood enters the relaxed heart chambers from the lungs and from the systemic circulation. Endogenous opioids: A group of brain chemicals that bind to opiate r e c e p t o r s in the brain, resulting in such effects as e u p h oria and pain relief; also contribute to alcohol r e i n f o r c e m e n t.

E n d o p h e n o t y p e :
A p h e n o t y p e that is not immediately visible but may contribute to the susceptibility to develop a particular behavior or syndrome.

E n d o t h e l i u m :
A layer of cells lining the inner wall of a blood vessel.

E n d o t o x i n :
A molecule in the cell wall of many bacteria, including many bacteria in the intestine. Endotoxins are released and may enter the bloodstream when the bacteria die; they can cause fever, chills, shock, and other symptoms of infection.

Epithelium:
The tissue layer lining the internal and external organs of the body as well as the blood vessels, body cavities, and glands.

Excitation-contraction (E-C) coupling:
The process through which the electrical excitation of a muscle cell membrane that occurs in response to a nerve signal leads to the contraction of the muscle cell.

E x t i n c t i o n :
The "un-learning" of a previously learned behavior (e.g., pressing a lever in order to receive alcohol); can be achieved by withholding the reward (i.e., alcohol) that was associated with the learned behavior.

Germ-line transformation:
A technique for introducing genetic changes into the germ cells (i.e., eggs or sperm cells) of an organism so that these changes are passed on to the offspring.

H e p a t o c y t e :
The principal cell type found in the liver; its many functions include bile production, p r o t e i n synthesis, detoxification, and nutrient storage.

H i p p o c a m p u s :
A curved ridge found within the cerebral hemisphere that functions in consolidating new memories.

Inbred strain:
A virtually genetically identical group of organi s m s derived by inbreeding among a limited number of ancestors. An inbred strain of mice is like a population of identical twins.
In vitro: Latin for "in glass," as in a test tube. An in vitro test is done in the laboratory using preparations of isolated cells, tissues, or organs.
Knockout/knock-in mice: Mice in which a g e n e has been deleted (knockedout) or m u t a t e d (knocked-in) in both the s o m a t i c and the germ cells so that the animals produce no functional gene product.

Kupffer cell:
A phagocytic cell in the liver that removes bacteria and other foreign organic substances from the blood by ingesting them.
Linkage study: A study that looks for g e n e s or a l l e l e s that are nece s s a r y or sufficient for the development of a particular disorder.

M i t o c h o n d r i a :
O r g a n e l l e s that generate the energy (e.g., adenosine triphosphate [ATP]) required for many cell functions.

M i t o g e n :
A molecule that stimulates cell division.

M u t a t i o n :
A change, deletion, or rearrangement in the D N A sequence that may lead to the synthesis of an altered p r o t e i n or to a totally inactive g e n e incapable of producing a protein.

M y o c a r d i u m :
A thick layer of uniquely constructed and arranged muscle cells that forms the bulk of the heart wall. Neuroadaptive changes: Changes in nerve cell gene expression and in the connections among nerve cells that occur in response to environmental changes (e.g., chronic exposure to alcohol or other drugs).

N e u r o p e p t i d e :
A small molecule that can regulate nerve cell function and is made up of amino acids.

N e u r o t r a n s m i t t e r :
A chemical messenger released by a nerve cell that transmits a nerve signal from that cell to a neighboring nerve cell.
O r g a n e l l e : A functional component of a cell (e.g., a m i t o c h o nd r i o n or the endoplasmic reticulum ); each organelle has its own membrane and specialized function.

O x i d a t i o n :
A chemical reaction that removes a hydrogen atom from a substance or adds oxygen to it (or both).

Oxidative stress: An imbalance between oxidants and a n t i o x id a n t s, leading to excessive o x i d a t i o n and cell damage.
Oxygen radical: Highly reactive, oxygen-containing molecules that cannot exist in a free state for a prolonged period; also called reactive oxygen species.

P a r a d i g m : A specific experimental design or approach.
Parietal cortex: A subdivision of the cerebral cortex involved in controlling higher cognitive functioning and the integration of sensory information.
Perfused organ: An isolated organ that is kept functional by passing a fluid (i.e., medium) through it.
Phagocytic cell: Any type of cell that eliminates foreign substances, microorganisms, or damaged cells by ingesting them.

P h e n o t y p e :
The observable properties, traits, or physical appearance of an organism resulting from the interaction of the g e n o t y p e with environmental factors.

Polymorphic marker:
A DNA marker that exists in different forms (i.e., a l l e l e s) within a test population.
Polymorphism: Occurrence of two or more a l l e l e s at a high frequency in the population Primary cell culture: In vitro cultivation of cells that have been newly isolated from an organism.

P r o m o t e r s :
Stretches of D N A associated with a specific gene that guide the expression of the gene to specific areas in the brain and "turn on" the expression of the gene. P r o s t a g l a n d i n s : A group of h o r m o n e -l i k e, unsaturated fatty acids that act in exceedingly low concentrations on a variety of organs, regulating, for example, heart function, smooth muscle tone, and nervous system function.

P r o t e i n :
The product of the genetic information encoded in a g e n e. Proteins are made up of amino acids whose order is dictated by the gene's nucleotide sequence.

Purkinje cells:
Specialized n e u r o n s in the c e r e b e l l u m that send signals from the cerebellum to other neurons after the cerebellar cortex has processed sensory and motor information from the rest of the nervous system.
Quantitative trait: A trait, or characteristic, that is determined by more than one g e n e and which exists in many different degrees (i.e., is distributed continuously) within a population. Body height is an example of a quantitative trait.

R e c e p t o r :
A protein that serves as a "docking molecule" for signaling molecules, such as n e u r o t r a n s m i t t e r s and hormones, and which mediates the actions of those signaling molecules.

Recombinant inbred (RI) strain:
An animal strain generated by mating two inbred strains and then inbreeding the F 2 ( " g r a n dchild") generation; in an RI strain, the genetic material from the original inbred strains has been recombined as a result of the D N A rearrangement that occurs during the specialized cell division (i.e., meiosis) that results in the production of egg and sperm cells.

Redox state:
The ratio of oxidized to reduced reactants in a cell.

Reinforcement:
A process in which a response or behavior (e.g., alcohol consumption) is strengthened by the anticipation of a reward (e.g., a feeling of euphoria).
Reverse genetics: Strategy in genetic research by which investigators begin by selecting a specific g e n e and then try to generate a mutant organism that lacks the function of that gene.

Somatic cells:
All cells of an organism other than the germ cells. Transcription factor: A p r o t e i n that binds to the D N A, regulating the conversion of genetic information into proteins.
Transformed cell line: A cell line, frequently derived from a tumor and grown in vitro, that no longer responds to normal growth control mechanisms and can divide indefinitely.
Transposable element: A small piece of D N A that can change its position in an organism's genetic material; if such a DNA piece by chance integrates into a g e n e, that gene (and the p r ot e i n it encodes) may be altered or even inactivated.
Transposon tagging: The process by which the known D N A sequence of a transposable element (i.e., P element) is used as a tag to isolate the genomic DNA located adjacent to the site of transposon integration. This procedure allows the cloning of the g e n e whose function is disrupted by the P element.

Tumor necrosis factor alpha (TNF-) :
A c y t o k i n e produced by a type of immune cell (i.e., macrophages) and which, among other functions, has anticancer effects.
V e s i c l e : A small, bubble-like component of the c y t o s o l that serves to store various types of molecules (e.g., n e r o t r a n s m i t t e r s) .